Some of these changes are a result of kernel changes, and some a
result of ipchains being different from ipfwadm.

Many arguments have been remapped: capitals now indicates a
command, and lower case now indicates an option.

Arbitrary chains are supported, so even built-in chains have
full names instead of flags (eg. `input' instead of `-I').

The `-k' option has vanished: use `! -y'.

The `-b' option actually inserts/appends/deletes two rules,
rather than a single `bidirectional' rule.

The `-b' option can be passed to `-C' to do two checks (one in
each direction).

The `-x' option to `-l' has been replaced by `-v'.

Multiple source and destination ports are not supported
anymore. Hopefully being able to negate the port range will somewhat
make up for that.

Interfaces can only be specified by name (not address). The
old semantics got silently changed in the 2.1 kernel series anyway.

Fragments are examined, not automatically allowed through.

Explicit accounting chains have been done away with.

Arbitrary protocols over IP can be tested for.

The old behavior of SYN and ACK matching (which was previously
ignored for non-TCP packets) has changed; the SYN option is not valid
for non-TCP-specific rules.

Counters are now 64-bit on 32-bit machines, not 32-bit.

Inverse options are now supported.

ICMP codes are now supported.

Wildcard interfaces are now supported.

TOS manipulations are now sanity-checked: the old kernel code
would silently stop you from (illegally) manipulating the `Must Be
Zero' TOS bit; ipchains now returns an error if you try, as well as
for other illegal cases.